For example, when using a CO.sub.2 analyzer for measuring alveolar air, a problem encountered is the water vapour contained in exhalation air. Since temperature in a sampling passage is lower than human body temperature, the water vapour condensates in a measuring device and the intrusion of water drops inside a measuring sensor results in the failure of a measurement. In addition, a gas ample often entraps mucus and blood as well as dust which the water separator must also be capable of removing from the gas.
In prior known gas analyzers, water has been removed from a gas sample by using a water separator, provided with a water-separation chamber which divides the flow into two partial flows in a manner that the main flow is sucked through a measuring sensor by means of a tube connected with the water-separation chamber and the many times lesser side flow is sucked continuously by way of a tube connected with the bottom section of said water-separation chamber into a water receiver for retaining therein the water contained in a gas sample and further on to a pump. This prior known solution involves the following drawbacks. The water-separation chamber results in extra volume in the passage of a gas sample, which leads to slower measuring. A drawback is also the failure of a water separation step. Inevitably, some water gets on a measuring sensor e.g. as a result of splshing in the separation chamber or some water finds its way to the pump after a water vessel in the side-flow branch is filled.
Another prior art method is the use of a moisture-equalizing tube. In this case, the analyzer is not usually fitted with an individual water separator but, instead, a sampling tube between a patient and the apparatus as well as a tube between s sampling connector in the apparatus and a mesuring sensor are made of a material which equalizes moisture of the gas inside the tube to be the same as that on the outside, so that water always tends to work its towards the drier side, the moisture of a gas sample equalizing to be the same as the moisture of ambient air and no condensation occurs on the tube walls.
This prior art solution involves the following drawbacks. The tube material is only capable of a limited transfer of water through the wall per unit time, whereby the water splashed from the tubing of a respiration apparatus, a patient's mucus or blood may end up on a measuring sensor. Dust in the air also finds its way to a measuring sensor and causes problems there.